The present invention relates generally to subterranean or underground construction techniques. More particularly, the present invention provides a method of efficiently forming a subterranean soil-cement casing. The casing may be used for a variety of purposes, including the insertion of reinforced high strength concrete into the casing.
It is known in the prior art to provide hollow cylindrical steel casings in a subterranean environment for a variety of purposes. These steel casings are typically hoisted and inserted into the hole on a piece-by-piece basis. The cost of installing underground steel casings can be extremely high and time consuming.
It is also known in the prior art to provide homogeneous, solid soil-cement support columns formed by a soil processing tool which utilizes high velocity cement slurry to create a soil-cement mixture. U.S. Pat. No. 4,958,962 teaches such a method.
There is a substantial need for underground casings which can be installed more quickly and less expensively than conventional steel casings. The present invention addresses that need and provides an underground casing comprised of a soil-cement mixture which can be formed much more quickly and much mare inexpensively than conventional steel casings. The present invention is an improvement over the methods disclosed in U.S. Pat. No. 4,958,962. The primary improvement over that patent is that the soil processing tool is vigorously rotated as it is removed from the hole, causing solids in the soil-cement slurry to migrate to the outer edges of the hole, so that the outer region of the mixture has a smaller proportion of free water. The denser solids include the relatively high strength cementitious solids and solid particles that form a much harder soil-cement mixture along the outer edges of the hole as compared with the center region. The lighter particles and water tend to remain in the center of the hole. The soil-cement column is allowed to set up and the soft center region is preferably drilled out, leaving the relatively hard and strong soil-cement casing in place. The hollow soil-cement casing may, in some forms of the invention, be filled with reinforced, high strength concrete. In other forms of the invention, the soft center region is left in place and not drilled out.
A primary object of the invention is to provide a method for producing underground cylindrical casings relatively quickly and inexpensively.
A further object of the invention is to provide a subterranean soil-cement casing which may or may not have its interior filled with reinforced high strength concrete.
Yet another object of the invention is to provide a method for forming subterranean soil-cement casings which may be of large diameter, i.e. greater than 20 feet diameter, great depth, more than 200 feet, and simultaneously having relatively large wall thickness, i.e. greater than 1 foot.